Gaming machines such as slot machines are popular among casino customers as devices through which customers can easily enjoy gambling and recent statistics indicate that income from gaming machines accounts for at least half of casino income. Early slot machines were simple devices that received inserted coins, and spun and stopped mechanical reels according to a handle operation, with a win or a loss determined according to a combination of symbols stopped on a single pay line. However, recent gaming machines have increased in sophistication to include mechanical slot machines in which physical reels are driven with high precision using computer-controlled stepping motors, video slot machines in which virtual reels are displayed on a display connected to a computer, and various gaming machines in which similar technology is applied to other casino games. For manufacturers developing these gaming machines, improving the functionality of gaming machines and providing highly attractive games that attract casino customers to play are important areas of focus.
In view of this background, a game machine that changes the symbol arrangement of a reel used for providing a normal game to a different symbol arrangement at the start of a free game provided without consuming any game value has been proposed. For example, the Patent Literature 1 discloses a slot machine in which when a normal game is provided, this slot machine uses reels having a symbol arrangement in which various types of symbols are randomly arranged and when a free game is started, this slot machine changes the reels into reels having a special symbol arrangement in which the same type of symbols are arranged to be adjacent to each other. In such a slot machine, the reels having special symbols arranged adjacent to each other are used when a free game is provided, therefore, the slot machine can increase the chance of winning based on the special symbols during the free game. In addition, since the special symbols arranged adjacent to each other are shown to the player, this can suggest a high level of winning expectation value, which enhances the expectation of the player in the free game.